Recently, a demand for precision management of a circuit line width required for semiconductor elements, has been increasingly high. A reduced projection lithography device referred to as a so-called stepper, exposes and transfers a pattern onto a wafer so as to form a circuit, using an original pattern including a circuit pattern formed (also referred to a photolithography mask or a reticle, and, hereinafter, referred to as a mask), so that the semiconductor elements are manufactured. Therefore, a pattern drawing apparatus using an electron beam capable of drawing a fine circuit pattern, is used in order to manufacture the mask for transferring the fine circuit pattern onto the wafer. The pattern drawing apparatus may be used so as to directly draw a pattern circuit onto a wafer.
Improvement of yields is necessary for the manufacture of LSI, such as a central processing unit (CPU) or a field programmable gate array (FPGA), involving significant manufacturing costs. One main cause that reduces the fields is a pattern defect of a mask used in exposing and transferring an ultra-fine pattern onto a semiconductor wafer with a photolithography technique. Recently, a scale required to be detected as a pattern defect has been considerably small accompanying with miniaturization of an LSI pattern scale formed on a semiconductor wafer. Therefore, a pattern inspection apparatus that inspects a defect of a transferring mask used in manufacturing LSI, preferably increases in precision.
A method of performing inspection by comparing an optical image including a pattern formed on a sample, such as a photolithography mask, captured with a predetermined magnification with a magnification optical system, and design data or an optical image including the same pattern on a sample, captured, has been known as an inspection method. Examples of a pattern inspection method, include “die to die inspection” including: comparing pieces of optical image data including the same pattern captured at a different position on the same mask, and “die to database inspection” including: inputting drawing data (pattern data) including CAD data including pattern design made, converted into an apparatus input format to be input by a drawing apparatus in drawing a pattern onto a mask, into an inspection apparatus, generating design image data (a reference image) based on the drawing data, and comparing an optical image including the pattern captured, being measurement data, to the design image data. In the inspection method with the inspection apparatus, a sample is mounted on a stage and then the stage moves so that a light beam scans on the sample and the inspection is performed. Alight source and an illumination optical system irradiate the sample with the light beam. Light that has passed through or reflected from the sample, forms an image on a photodetector through an optical system. The image captured by the photodetector is transmitted, as measurement data, to a comparative circuit. The comparative circuit compares the measurement data and the reference data in accordance with an appropriate algorithm after positioning between the images, and determines that a pattern defect is present when inconsistency is acquired.
The pattern inspection apparatus described above, irradiates a substrate with a laser beam and then captures a transmitted image or a reflected image of the laser beam so as to acquire an optical image. In contrast to this, an inspection apparatus that irradiates a substrate with an electron beam and detects a secondary electron emitted from the substrate so as to acquire a pattern image, has been also progressively developed. Patent Document 1 discloses a technique of capturing a previously set region for a plurality of dies formed on a sample, acquiring a SEM image, and producing an average image of the SEM image for a reference image.